The long term goal of the proposed research is to use biochemical and cell biological approaches including morphological (transmission electron microscopy, scanning electron microscopy, autoradiography, x-ray microprobe analysis, fluorescent antibody studies, fluorescent photobleach) and cell fractionation techniques to analyze structurally and functionally the integrative mechanism by which hormones regulate adipocyte metabolism. In particular, emphasis will be placed on understanding the mechanism of insulin action. The key areas to be studied will include: a) Insulin-receptor interactions using 125I-insulin, monomeric ferritin-insulin, monomeric ferritin-125I-insulin and monomeric 125-I-ferritin-insulin to study hormone binding and degradation and their relationships to biological activities. In addition these agents will be used to study the fate of the insulin receptor and the possible internalization of insulin or pieces of it. b) To characterize the hormonal alterations of calcium content in various subcellular compartments by electron histochemical techniques and x-ray microprobe analysis. Biochemical studies in this laboratory have documented the ability of insulin treatment of fat cells to alter the calcium content and metabolism by various subcellular compartments as well as demonstrated an active insulin-sensitive calcium uptake system in the endoplasmic reticulum.